The present invention is directed to a regulated dental turbine having an arrangement for directing a volume stream of a drive fluid onto a turbine disc or wheel and includes an arrangement for regulating the speed of the turbine wheel.
Two types of drives are principally utilized at present in order to do justice to different preparations in the dental practice. One of these drives is a turbine drive, which has extremely high no-load speeds which are 300,000 RPM. The other type of drive is an electric or air motor which has a lower speed in comparison to turbine speeds and up to a maximum of approximately 200,000 RPM.
Dental turbines have the advantage of a relatively simple structure and simple supply, but are burdened, however, by the disadvantages of a relatively low drilling power and of a high no-load speed that drops greatly when loaded by an external load or moment M. A relatively high wear and the risk of burning dental substances are also consequences of this high speed.
Although electric or, respectively, air motor drives will supply adequate torque and drilling power, the optimum speed in a range of 180,000 RPM through 200,000 RPM can only be achieved with considerable technological outlay with many rapidly moving parts, which has the consequence of a correspondingly high wear, relatively high weight and relatively high cost.
These different properties require that the dentist currently usually requires both types of drives in one treatment unit.
In order to avoid a decrease in the speed under loads given dental turbines, it has already been proposed to keep the speed constant independent of load. U.S. Pat. No. 3,865,505, whose disclosure is incorporated herein by reference thereto, discloses a controllable turbine of this type. In this patent, a valve is arranged in the delivery channel of the driving compressed air, and this valve is controlled by the volume throughput of the return air. When the speed of the turbine drops, due to the external load, then the valve in the delivery channel is opened and a larger air volume is, thus, conducted to the turbine. The control of the admission air stream, dependent on the returned air, can occur in various ways in the known turbine. Among these ways are a spring-loaded slide in the returned air channel that controls the valve in the delivery channel or can occur via a diaphragm-type barometric cell arranged in the returned air channel that adjusts a piston which controls the flow in the delivery or admission channel.
Among other things, the known turbine is effected with the disadvantage that relatively great forces are required for throttling the overall air stream. These relatively great forces are capable of being provided in the exhaust air channel only upon utilization of volume and mass. An unstable control behavior of the turbine, however, is, thus, created. In addition, the known arrangement causes a relatively large structure within the turbine handpiece, as a result whereof the integration problems can occur.